1. Field of the Invention
The present invention relates to an axial air gap type rotary electric machine such as printed circuit motor, multi-phase alternator and flat motor. More particularly, the invention is concerned with an improvement in a cooling mechanism of the rotay electric machine of the class specified above.
2. Description of the Prior Art
The rotary electric machine of the class specified above is provided with a flat coil comprising an annular carrier member of an electrically insulating material and windings carried by the carrier member. The windings are formed by a plurality of annular rows of generally radially extending and axially thin conductors each having radially inner and outer end sections and an intermediate section. The flat coil is disposed in the axial air gap type rotary electric machine such that the opposite sides or end faces of the flat coil are faced towards magnets. More specifically, in the case of an axial air gap type generator, the flat coil is employed as a stator coil and has opposite end faces disposed in opposite relationship to magnets carried by a pair of rotors mounted on a shaft for rotation therewith so that, when the rotors are rotated with the shaft, the flat coil cooperates with the magnets to generate induced electromotive force. Further specifically, only the intermediate sections of the conductors of the flat coil are faced toward the magnets of the rotors and effective to produce the electromotive force. Thus, the intermediate section of each conductor of the flat coil is termed herein as an "effective section".
The windings of the flat coils of the prior art axial air gap type rotary electric machines were formed either by wires each having a round cross section of a uniform diameter throughout its length, as seen in flat motors, or by conductor segments each having a uniform axial thickness, as seen in printed circuit motors. Because of the structure of the flat coil of this kind of rotary electric machines, the flat coil had a problem that the radially and axially inner parts of the flat coil could not easily be cooled and thus suffered from a high or elevated temperature. In addition, because modern printed circuit motors, flat motors and alternators are designed to have reduced sizes and to produce increased outputs, the heat produced in the entireties of the flat coils used in these rotary electric machines tend to increase compared with the heat produced in the relatively large-sized prior art rotary electric machines. Thus, it is now required to prevent the temperature rise in the flat coils of the axial air gap type rotary electric machines.
U.S. Pat. No. 3,231,774 discloses a three-phase armature coil formed by an annular disc or carrier member and three-phase windings caried by the carrier member. In making a generator or motor of a large capacity by such a three-phase armature coil as dislcosed in the U.S. patent referred to, a plurality of such annular carrier members are stacked to form a laminated structure and the windings are connected in parallel relationship to each other to increase the output.
U.S. Pat. No. 3,500,095 discloses a laminated structure of a flat DC motor armature coil which is adapted to be supplied with a DC current from a brush unit.
In a rotary electric machine having such a laminated or multi-layered structure of flat coil, temperature rise is caused particularly in the axially inner parts of the annular effective zone of the flat coil. In an attempt to solve this problem, if the cross-sections of the generally radial conductor segments of the flat coil are increased to decrease the density of the current passing therethrough, the axial distance between the magnets disposed on the opposite sides of the flat coil is undesirably increased to increase the magnetic reluctance of the path of the magnetic flux produced by the magnets, with a resultant disadvantageous problem that the efficiency of the rotary electric machine is lowered.